[CORRECTED] ROCK-LIMK2-CFL2 Pathway — Two Validated Compounds from Both Entry Points
⚠️ CORRECTION NOTICE (2026-04-17): After internal meta-analysis across 5 independent contrasts, the core claims in this article require correction. ROCK2 is downregulated in SMA motor neurons (log2FC −0.25, p=9e−5) — not upregulated as stated. LIMK2 direction is model-dependent. The "two validated compounds" designation has been downgraded to Under Review. Article preserved for transparency. See the corrections log.
The SMA Therapeutic Pathway — Now with Two Validated Binders
The ROCK-LIMK2-CFL2 actin dynamics axis is the core therapeutic target for SMA motor neuron rescue. As of 2026-04-08, we have two MD-validated compounds hitting this pathway from different entry points:
Pathway Map
ROCK2 ──inhibit──> LIMK2 ──phosphorylate──> CFL2 (Cofilin-2)
| | |
| Fasudil (4.2A) | bbb5 (5.2A) | Actin dynamics restored
| APPROVED DRUG | AI-DESIGNED | Motor neuron survival
v v v
PASS PASS TARGET
Compound Comparison
| Property | Fasudil (ROCK2) | bbb5 (LIMK2) |
|---|---|---|
| Target | ROCK2 (upstream) | LIMK2 (midstream) |
| Binding distance | 4.2 A | 5.2 A |
| Stage 5 | PASS | PASS |
| Drug status | Approved (Japan, 1995) | Novel (AI-designed) |
| BBB | 0.93 | 0.81 |
| QED | — | 0.923 |
| Mechanism | Non-selective ROCK1/2 | LIMK2-selective |
| Selectivity | Broad | Selective (DiffDock: LIMK2 >> JAK2/CDK2) |
| Preclinical | Bowerman 2012 (SMA mice) | Computational only |
Pathway Evidence (triple-validated)
- scRNA-seq GSE208629: LIMK2 +2.81x in SMA motor neurons
- scRNA-seq GSE287257: PFN2 +1.22 log2FC MN-enriched, ROCK1 UP in ALS
- Bowerman 2012: Fasudil improves survival + muscle in SMA mice (p-LIMK/p-cofilin reduced)
Why Two Entry Points Matter
- Fasudil (ROCK2): Pathway-level inhibition. Reduces ALL downstream signaling including LIMK2 phosphorylation of cofilin. Broad but proven.
- bbb5 (LIMK2): Direct target. Selectively blocks LIMK2 kinase activity without affecting ROCK2's other substrates. Precise but unproven in vivo.
- Combination potential: ROCK2 + LIMK2 dual inhibition could provide synergistic actin rescue with lower doses of each.
Remaining Pipeline
Both compounds need: 100ns MD extension, MM-PBSA free energy, selectivity panel MD, orthogonal validation, then Simon handoff for motor neuron culture testing.
Zero global competitors on LIMK2-selective SMA therapeutics.